fix(backup): set backup error if backup target invalid

When starting a backup monitor, it will start to take a snapshot
backup procedure and it will be failed if the s3 backup target is
invalid (nfs backup target will be not be failed because of timeout
and test the backup when it is in progress.)
Set the backup state as `Error` if starting the backup procedure
returns an error.

Ref: 1249

Signed-off-by: James Lu <james.lu@suse.com>
(cherry picked from commit e278ba0)

controller/backup_controller.go

@@ -375,6 +375,10 @@ func (bc *BackupController) reconcile(backupName string) (err error) {
 
 		monitor, err := bc.checkMonitor(backup, volume, backupTarget)
 		if err != nil {
+			if backup.Status.State == longhorn.BackupStateError {
+				log.WithError(err).Warnf("Failed to enable the backup monitor for backup %v", backup.Name)
+				return nil
+			}
 			return err
 		}